1. Field of the Invention
The present invention relates to a solid waste disposal apparatus and, more particularly, to an apparatus to be used for the on-site disposal of waste material at the source where it is generated rather than in a large, central facility.
2. Description of the Related Art
The disposal of infectious clinical laboratory waste has become a major problem. In coastal areas, for example, improper waste disposal has recently caused major disruptions on beaches. The disposal of hazardous chemical laboratory wastes has been controlled by regulations for a number of years. Most regulations require that such waste be disposed of under a manifesting system wherein responsibility for the waste is clearly defined at all stages of its progress from the source to the ultimate disposal destination, either in an incinerator or in a certified hazardous waste landfill. Similar regulatory approaches are in the process of being implemented in a number of locations for infectious medical wastes in response to the disposal problems recently encountered.
A significant portion of medical wastes, particularly those from hospitals, are often disposed of in on-site incinerators. Some of these devices are in compliance with applicable codes, others are questionable or clearly noncompliant. Most smaller laboratories, such as independent clinical laboratories, contract with licensed hazardous waste haulers who move the material to an off-site central incinerator facility and dispose of it under certified conditions.
The magnitude of the waste disposal problem can be judged from the fact that the total of so called "Regulated Medical Waste" generated nationwide is reported to be approximately 700,000 tons per year. The cost of disposal by off-site hauling has been approximated to be $1,250.00 per ton for a total cost of $850,000,000.00 nationwide. These "Regulated Medical Wastes" include the following:
Cultures and stocks of infectious agents and associated biologicals, including specimen cultures, culture dishes and related devices, biological production wastes, and discarded live and attenuated vaccines. PA1 Bulk blood, blood products, and body fluids. PA1 Pathological wastes, such as tissues, organs, body parts, products of conception. PA1 Needles, syringes, intravenous tubing with needles attached, vacuum collection containers and tubes containing blood and blood products. PA1 Carcasses, body parts and bedding of research animals exposed to pathogens. PA1 Waste from rare or unusual cases of communicable diseases. PA1 a. simplicity in operation comparable to a household appliance PA1 b. substantially free from air emissions PA1 c. ability to handle a wide range of waste material including paper, liquids and plastics including chlorinated plastics PA1 d. maximum reduction in mass and volume of the waste. Although requirement d can only be met by thermal destruction of the waste, requirements a, b and c together rule out conventional incinerator approaches based on burning waste with air. Even more sophisticated two stage incinerators in which the waste is burned with deficient air, and the combustion gases are afterburned in a secondary chamber, cannot meet the requirements.
Almost as serious a problem in urban areas is the disposal of household solid wastes. These, while nonhazardous and not requiring the extreme care in manifesting and maintenance of responsibility as required for hazardous and infectious waste, require disposal either in landfills or incinerators, procedures that are encountering serious difficulties in many locales. Landfills are by far the least expensive alternative; but landfills in most urban areas are being exhausted and shut down continually and new landfill sties are often opposed by the local residents. Incinerators are viewed as being extremely expensive to build and operate and are opposed, if anything, even more vigorously by the local residents. A disposal solution that has been adopted frequently has been to transport waste further and further from the source of origin into neighboring areas, and as a consequence, disposal costs have increased.
As such, the on-site disposal of solid waste has been recognized by many as a promising solution to most of the aforementioned disposal problems. Many of the cost factors associated with transporting and tracking the waste are reduced significantly. Also, expensive landfill capital and operating costs are virtually eliminated. Although those concerned with the development of waste disposal equipment have long recognized the need for an on-site apparatus for general use, no practical, economic device has yet been proposed. The requirements which such a device must meet are:
Commercial pyrolysis waste disposal systems have been available for some years as indicated in Zeltner, K.A.; Pyrolytic Processing of Organic Wastes; Proceedings of the 37th Industrial Waste Conference, pp. 21-18 (1983). These devices are usually large industrial units, custom designed for each application, and the number of installations so far is limited. Pyrolysis occurs in these devices on a rotary hearth direct fired with stoichiometric gas-air burners to provide an approximately oxygen-free atmosphere. No attempt is made to combust the carbon in the residue which is discharged directly with a reduction in mass relative to the feed of 80%.
Typical hospital incinerator systems, described by Tessitore and Cross; Incineration of Hospital Infectious Waste; Pollution Engineering, Volume XX, Number 11, pp. 83-88, November 1988, and Marks, C. H.; Burn or Not to Burn: The Hospitals'Modern-Day Dilemma; Pollution Engineering, Volume XX, Number 11, pp. 97-99, November 1988, operate on the controlled air principle in which the primary combustion chamber operates with deficient, but not zero, air to reduce particulate emissions, and the gases are burned to completion in an after-burner. In this type of incinerator the combustible content in the ash can be reduced by 5%, but with significant fly ash emissions. The same principle is used in modern wood stoves.
Nine innovative thermal destruction approaches have been described in Freeman, H.; Innovative Thermal Processes For The Destruction of Hazardous Wastes; AIChE Symposium Series, Separation of Heavy Metals, No. 243, Vol. 81 (1985), including approaches in which heat was transferred to the incoming solid refuse by a molten salt and molten glass. None of these techniques have achieved commercial acceptance nor are any of them suitable for the present application.
U.S. Pat. No. 3,639,111 of David L. Brink and Jerome F. Thomas discloses a system for pyrolysis of black liquor from the Kraft process with sequential pyrolysis chambers in which the waste was heated first indirectly and then directly. A controlled amount of air was introduced into the pyrolysis zone to achieve the requisite cracking temperature. The process is complex and specialized.
Mitsui Engineering and Shipbuilding patented in Japan (Japanese Patent No. 80/65,817) a system for radioactive wastes in which the wastes were indirectly heated to thermal decomposition followed by combustion of the pyrolysis vapors to completion. The method was described as applicable to both continuous and batch operation and was reported to produce little dust. Mitsui's patent recites application of their process to ion exchange resins and other polymers, paper, cloth and wood. The process is potentially applicable to on-site destruction of waste, but it has no provision for completely combusting the carbonized residue to an ash.
Pyrolysis is particularly applicable to the destruction of wastes containing halogens such as Cl and Br. Pyrolysis and incineration of difficult to combust organic residues is disclosed in U.S. Pat. No. 4,255,590 of John K. Allen. This patent recites pyrolysis in a fluid bed of sand fluidized by nitrogen followed by incineration of the off-gases. After removing condensable hydrocarbons, halogen acids are absorbed by a carbonate, hydroxide, or oxide of calcium and magnesium. This process was invented to dispose of waste from the manufacture of benzene di- and tri-carboxylic acids. It is not suitable as an on-site approach in that it is a complex, continuous process carried out in a fluid bed which is notoriously difficult to control and operate.
Pyrolyzing polyvinylchloride plastic to avoid formation of phosgene is described in U.S. Pat. No. 4,399,756 to la Clede Lientz. This process is also continuous and also introduces deficient air into the pyrolysis zone which restricts the types of waste that can be handled.
In U.S. Pat. No. 3,788,243 of Christian A. Eff, an incinerator for domestic refuse is described. This device heats the partially combusted gases from incomplete combustion of waste electrically with addition of excess air to complete combustion. It shows some of the batchwise electrically heated features needed in an on-site device. This device is likely to have significant air emissions. Also, it is limited in the types of waste material it can handle because the waste material is used as the fuel.
In U.S. Pat. No. 4,350,102 of Hans Ruegg, there is disclosed a system wherein the generation of combustible gas is controlled by controlling the heat input to the pyrolysis section. In this case, however, heat input is controlled by admitting or not admitting air for combustion to the pyrolysis chamber manually. This device is, therefore, complex to operate and the types of waste material it can handle are limited.
As can be seen from these descriptions of prior art disposal apparatus, there is an unmet need for a practical on-site disposal device of general utility. The present invention fulfills this need.